Method of reducing the diameter of apertures

ABSTRACT

A SYSTEM HAVING MEANS FOR CLEANING AND ELECTRODEPOSITING A LAYER OF MATERIAL ON A FORMED TELEVISION MASK IN A CONTINUOUS ASSEMBLY LINE TECHNIQUE TO CONTROLLABLY REDUCE THE DIAMETER OF THE APERTURE SO THAT THE MASK CAN BE USED AS A PATTERN FOR LAYING A PHOSPHOROUS DOT PATTERN ON THE FACE PLATE OF A TELEVISION TUBE.

April 30, 1974 J, FRANTZE'N vFETAL METHOD OF REDUCING THE DIAMETER OF APERTuREs 4 Sheets-Sheet 1.

Original Filed June 50, 1969 INVENTORS JOHN J. FRANTZE/V CLIFFORD J [WK/(OLA ATTORNEYS April 30,1974 u J. FRANT'ZE'N ETAL 3,808,107

' METHOD OF REDUCING. THE DIAMETER 0 APERTURES 4 Shee t-s-Sheet 2 Original Filed June so; 1969- flamw mm hm mm. mm

v' P 3 1974 J.J. FRANTZEN T 3,808,107

METHOD OF REDUCING THE DIAMETER OF APERTURES Original Filed June 50, 1969 4 Sheets-Sheet 5 INSPECTION STATION .COOLING AREA DRYING OVEN SPRAY RINSE ZINK PLATING TANK April 30, 1974 JHJ, FRANTZEN ETAL 3,808,107

METHOD OF REDUCING THE DIAMETER OF 'APERTUREs Original Filed June 30, 1969 v 4 Sheets-Sheet .1

United State Paenf'ome Us. 01. 204-24 Claim ABSTRACT OF THE DISCLOSURE A system having means for cleaning and electrodeposit- 3,808,107 Patented Apr. 30, 1971 One of the problems involved with temporarily stepping down the aperture size and plating a second material on top of the mask is that the shadow mask is usually in a pre-formed dome-shape having an outer welded frame. This dome shaped mask is difficult to plate as it tends to plate unevenly 'because of the dome-shape ing a layer of material on a formed television mask in a continuous assembly line technique to controllably reduce the diameter of the aperture so that the mask can be used as a pattern for laying a phosphorus dot pattern on the face plate of a television tube.

This is a division, of application Ser. No. 837,648, filed June 30, 1969 and now abandoned.

. BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to shadow masks for colored television tubes and, more particularly, for a method and system for temporarily reducing the diameter of the apertures of a formed or domed shadow mask so the domed mask can be used as a pattern for printing phosphorus dot patterns on the face plate of the colored television tube. v

Description of the prior art During the'assembly of the picture tube the shadow mask is used as a mask or master pattern for forming the phosphorus dot pattern on the face plate of the television tube. This is usually done using photographic techniques which are well known in the industry today. In order to produce a picture with a maximum possible brilliance at the face of the tube when the phosphorus dots are struck by the electron beam and at the same time focu's ing properly on the particular phosphorus dot, or dots, it is necessary in certain instances to have the phosof the apertures of the shadow mask. To facilitate the screening of the phosphorus dot pattern with existing apertures of the shadow mask requires a temporary stepping down or reduction in 'the 1 diameter of the apertures by partially filling the apertures ger of removing the first material. After using the mask for forming the pattern for laying the phosphorus dot pattern on the face plate of the tube, the filling material can be removed to enlarge the holes in the aperture mask to the original size so that the maximum brilliance can be obtained from the television tube.

which traps gases by the surface of the mask. This results in uneven or even no plating in local areas. Also, if the technique of plating to fill the holes is used on a production line basis it is necessary to remove foreign materials from the masks prior to electrodepositing as well as any harmful gases that are evolved during the plating action. This is particularly true if the plating material to be applied to the mask is material such as zinc.

Also, in order to insure that the phosphor dot pattern can be properly formed, it is necessary to accurately control the diameter of the apertures. In a typical plating operation this means that an operator must control the hole size to within .0002".

The present invention overcomes these prior art problems and provides a complete automated system that prepares the mask for plating as well as plating in one continuous assembly line operation.

BRIEF SUMMARY OF THE INVENTION Briefly, the present invention comprises a system and method for cleaning, neutralizing and plating a domeshaped mask to reduce the diameter of the apertures in a uniform manner so that the mask can be used as a pattern for forming the phosphorus dot pattern on the face plate and the mask can then be etched to remove the top layer of material on the dome-shaped mask.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIGS. 1a, 1b and 1c show in semi-diagrammatic form a front elevation view of a plating system 10 and FIGS. 2a, 2b and 20 show in semidiagrammatic form a top view of plating system 10. Briefly, plating system 10 comprises an electrocleaner station or unit 20 for removing any organic or foreign material from a dome-shaped mask 15. Since all the masks are identical, they will all be referred to by a common reference numeral 15. Typically, electrocleaner station 20 contains ahot caustic or alkaline solution which can be applied to mask 15 by either dipping the mask phorus dots smaller in diameter than the final diameter in the solution or spraying the solution on the mask. The next station is a water spray station 21 that sprays water through nozzles 21a to rinse off any caustic solution that clings or adheres to the mask. The purpose of the rinse'station is to prevent any contaminants or solution from being carried from one work station to an adjacent work station and thus contaminating the adjacent work station.

' 'Located afte'r spray station 21 is a station 22 that containsa nitric acid bath for removing any rust or metallic oxides that are present on dome-shaped mask 15. Typically, the masks are made from cold rolled steel which is susceptible torust. Next, dome-shaped mask 15 passes from the nitric acid bath into a water spray rinse station 23 that rem'oves'any nitric acid that is adhered to the mask by spraying water onto the mask through nozzles 23a.

station 24 that neutralizes the surface'of the mask 'to" prepare the surface so that a flash base layer of plating material can be applied to the mask. The purpose of the base layer is to provide a better surface for receiving the depositant. In certain instances, this additional step of neutralization and applying a flash layer could be eliminated and the filler material could be deposited directly on the mask. Located immediately after cyanide dip station 24 is a deionized water spray rinse station25 that removes any cyanide solution that is adhering to the mask by spraying deionized water through nozzles'25cz. After spraying mask 15 with deionized water the mask moves into a drying chamber 26 where the mask is heatedby' a warm air from heating coils 26 a until the mask is dry,

The next station is a plating tank 27 where the mask is immersed in a plating solution andplated with a flash or very thin base layer of material such as copper. Typically, the thickness of this plating material may be about two millionths of an inch. Although copper is preferred sen forms a smooth conducting base for electroplating it is apparent that other material which forms a good conducting base could equally well be used. A

After plating the base material on the mask atstation 27, the mask enters a rinse station 28 where any excess plating solution is rinsed off the mask by spraying water through nozzles 28a.

After leaving rinse station 28 the mask enters an elongated plating tank where the mask is electrodeposited with a suitable plating material until the diameter of the holes is approximately one-half of their previous diameter. Typically, a variety of different filler materials that plate with a fine grain could be plated on the mask to reduce the diameter of the apertures. Gold and silver are examples of other material that could be used but these materials are relatively expensive to use in comparison to zinc which is the preferred filler material.

After passing through the zinc plating station the mask passes into a spray rinse station that rinses off any con,- taminants that may have been picked up in the zinc plating station by spraying water through nozzles 30a. Next, the mask passes into a drying station 31 and from there into a cooling station 32 and from there into an inspection station 33 which the mask can be expected to determine if the openings are the proper size. This briefly describes the various stations and their action and relation to the whole system. The particular features of the system which aid in producing an etfective reduction of the mask size will now be described in more detail.

Referring to FIG. 3, a portion of plating tank 29 is shown in cross-section. Located within plating tank 29 is an elongated circular anode 40 for depositing and'directing the plating solution onto the mask.- Located around anode 40 is an anode shield 41 that flares outward to direct the depositant onto the mask. By having a shaped anode and anode holder arrangement as shown in FIG. 3, it ensures that the depositant is properly circulated through the plating solution to produce an even layer of depositant on the mask. Anode 40 comprisesa set of spheres 40a that are located adjacent to one another in cylindrical anode holder 42. Although spherical anodesare shownand used for convenience in replacing the anodes, other shapes of tion of plating tank 29 there are similar sets of adjustable anodes and 'an'ode holders located in a spaced relationship on opposite sides of plating tank 29. This allows the operator to adjust each anode holder to increase or decrease plating action in localized areas of the preformed dome-shaped mask. By adjusting the anode holders through a trial and error process, the operator quickly obtains the proper position of the anode holders that is necessary in order to plate the dome-shaped mask. Sometimes it is preferred to plate the filler material in an uneven or graded pattern. With the present setup of adjustable anode holders it is apparent that this can also be readily accomplished.

In order to keep the plating solution within station 29 free from impurities and to maintain the system in a clean condition, the surface liquid on top of station 29 is continually skimmed off through outlets 70 and 71. As the old surface liquid is skimmed off, clean plating solution is supplied to station 22 through lower inlets 72 and 73 from a suitable supply source (not shown). The plating solution within tank 29 is controlled through an external apparatus (not shown) that monitors the temperature of the solutions, the pH of the solutions as well as filtering the plating solution through a .5 micron filter. By monitoring, controlling and filtering the plating solution, an operator can ensure that a' homogeneous plating solution is present within plating tank 29.

In addition to plating the mask from a number of anodes to obtain the desired plating pattern, a set of pressure actuated cylinders 11 move laterally back and forth as the masks move longitudinally through plating tank 29. This lateral movement aids in freeing any gas bubbles that may be trapped on the surface of the mask which would produce a localized area having no plating thereon. The transverse movement of the dome-shaped mask 15 is accomplished in the present invention by pressure actuated cylinders 11 that automatically, through means (not shown), move the entire overhead track 13 in a lateral direction. However, other methods of moving the masks laterally are envisioned such as a zig-zag or cured track that the mask support would follow. Located in the top portion of tank 29 (FIG. 3) is a pair of exhaust ducts 51 and 52 that are suitable for attachment to a gas discharge I pump (not shown). Similarly, located on the opposite side of tank 29 are a pair of exhaust ducts (not shown) which are also suitable for attachment to a gas discharge pump. In operation the pump draws atmospheric air from above the plating tank and through the exhaust ducts to produce a continually moving sheet of air over the plating solution. This sheet of air entrains any harmful gases that are evolved from the plating action and discharges them into an atmosphere where they will not harm anyone; These exhaust ducts are located along the entire top length of station 29 so as to produce a continuous moving sheet of air over the entire plating tank 29.

Referring to FIG. 4, a mask carrier 12 is shown for supporting, lifting and turning a dome-shaped mask which is shown partially cut away. Mask carrier 12 comprises a anodes could also be used. Anode holder 42 has a pair of electrical leads 42a that connect to a suitable sourceof energy. Located on each end of anode holder-42'is a pivotal support member 43 having a pivotal member 43a that rotatably supports anode holder 42 in tank 29. An adjustment lever 44 extends from anode shield 41 upward and out of tank 29 to allow an operator to rotateanode 42 without having to immerse his hand into theplating solution in tank 29. In order to prevent undue; rotation of anode holder 42 there is provided a stop member 45 having a screw 45a that can be tightenedtojfrictionally engage anode holder 42 to prevent rotation of anode 42 during the electrodeposition process. In a typical construcmember 55 that attaches to chain 56, a vertical slidable support arm 57 and a cross arm 54 for supporting mask 15. Located on member 55 is a pressure actuated cylinder 58 that connects to a pressure source (not shown). Cylinder 58 has an extendible rod 58a which connects to slidable rod 57 through circular slotted lift plate 60. Applying a pressure signal at inlet 61 on pressure cylinder 58'extends rod 58a vertically upward which also raises vertically slidable rod 57 and mask 15 out of the particular work station. Similarly, applying a pressure having a self contained pressure supply unit moving with the track. Other alternative embodiments are envisioned which would perform the same functions but with a different mechanism. For example, the individual pressure cylinder could be attached to an overhead mechanism to lift the masks upward when the masks reach a predetermined position or the individual pressure cylinder could be eliminated and the entire track could be lifted vertically upward through simultaneously raising and lowering all the masks.

As the masks proceed through plating station 29 they are turned 180 when they reach the middle of plating station 29. One of the purposes of rotating the mask 180 is to minimize any unevenness in plating which might be produced by asymmetries in the tanks. Typically, the mask is raised upward from the tank by applying a pressure signal to pressure cylinder 58. When the mask is in the raised position an operator can easily rotate support 57 and mask by merely pushing on support 54. The circular slotted plate 60 allows rod 58a to slide inside the circular slot until the mask is rotated. While the mask could be rotated while it is in the tank, it is preferred to raise the mask out of the plating solution so that any gases that might be trapped by the surface of the mask can be released.

As all the mask carriers and lifting mechanisms for each mask are identical, only one of them has been described.

Because mask 15 contains a rather massive frame around the mask which would conduct current more readily and thus attract more depositant to the heavier frame than the face plate of the mask, it is necessary to place a shield 60 around the outer edge of mask 15. Shield 60 also prevents excessive depositant from being plated on the sides of the mask frame.

In addition to rotating the mask at one interval in the plating tank, the mask could be rotated continuously as it passes through the tank to thus ensure the desired plating action. This would have the effect of changing the mask in relation to the particular set of anodes so as to eliminate undesirable localized plating actions.

We claim:

1. The process of reducing the diameter of a plurality of apertures which are located in a preformed domed shadow mask comprising the steps of:

cleaning the preformed domed mask in a hot alkaline solution to remove any organic material on the surface of said domed shadow mask, rinsing said domed shadow mask to remove any alkaline solution on the surface of said domed shadow mask as a result of the step of cleaning said domed shadow mask with an alkaline solution, cleaning the surface of said domed shadow mask with a nitric acid solution to remove any oxides on the surface of said domed shadow mask, rinsing said domed shadow mask to remove any nitric acid solution remaining on the surface of said domed shadow mask as a re sult of cleaning of the surface of said domed mask with a nitric acid solution, cleaning said domed shadow mask in a cyanide solution to neutralize the surface of said domed shadow mask for receiving a flash layer of plating material, rinsing said domed shadow mask to remove any cyanide solution on the surface of said domed shadow mask as a result of the step of cleaning the surface of said shadow mask with a solution of cyanide, drying said domed shadow mask, plating said domed shadow mask with a flash layer of base material to form a smooth electroplating conducting base on said shadow mask by immersing said domed mask in a flash plating solution, rinsing said domed shadow mask to remove excess flash plating solution from the surface of said domed shadow mask, electroplating a layer of zinc on top of said flash layer of base material to thereby reduce the diameter of the apertures in said domed shadow mask by circulating the zinc plating solution through a zinc plating tank during immersion of said domed shadow mask in said zinc plating tank, agitating said domed shadow mask in said zinc plating tank by moving the mask laterally to thereby force plating solution through the apertures of said shadow mask and thereby remove any air bubbles adhering to the surface of said domed shadow mask, and rotating the mask in the plating solution to thereby produce a uniform layer of zinc material on said domed shadow mask, said layer of zinc material partially filling the apertures in said domed shadow mask to thereby reduce the diameter of the apertures in said domed shadow mask and rinsing said domed shadow mask to remove any zinc plating solution on said domed shadow mask, drying said domed shadow mask, cooling said domed shadow mask and inspecting the apertures in said domed shadow mask to determine if the apertures of said domed shadow mask are reduced to the proper dimension.

References Cited UNITED STATES PATENTS 3,231,380 1/1966 Law 204-24 1,795,081 3/1931 Davis et a1 204 R 3,532,801 10/1970 Faulkner 20415 1,715,357 6/1929 Hall 204202 THOMAS M. TUFARIELLO, Primary Examiner US. Cl. X.R. 

